Heat exchanger

ABSTRACT

A heat exchanger having a polyamine on at least part of a surface of the heat exchanger. The existence of polyamine on the surface of the heat exchanger allows the odor components to be temporality held by virtue of the action of polyamine, and the odor components are not released into an interior room or the like at once in conjunction with the evaporation of free water (such as condensed water). Thus, the release of odor components is made moderate, and changes in the concentration of odor components in the interior room are reduced, so that strong odors sensed by people are suppressed. A typical example of the polyamine is PEI, and a typical example of the heat exchanger is an evaporator used in a car air-conditioner.

TECHNICAL FIELD

The present invention relates to a heat exchanger that can suppress odors sensed by people in an interior room or the like.

BACKGROUND ART

Interior rooms of buildings, moving vehicles, etc. are usually provided with air-conditioning apparatuses (referred to as “air conditioners”). Air conditioners introduce air having passed through heat exchangers into interior rooms to adjust the temperature and humidity in the interior rooms.

People in such interior rooms may sense odors even when a strong odor source is not present. Causes of such odors may often be odor components released at certain timing from air conditioners (in particular, from built-in heat exchangers) in addition to odor components released from wall surfaces and the like.

Countermeasures against such odors (deodorization measures, odor suppression measures) have been adopted, including removal of odor components causing the odors, such as by adsorption, decomposition, or washing. In addition, in the case of a member (apparatus) that generates a large amount of condensed water on the surface, such as an evaporator for an air conditioner, it has also been proposed to perform surface treatment with a treatment agent (such as (modified) polyvinyl alcohol) that has low affinity with odor substances (odor components) and excellent hydrophilicity. Descriptions relevant to this are found, for example, in the following patent documents.

PRIOR ART DOCUMENTS Patent Documents

-   [Patent Document 1] JP2002-285139A -   [Patent Document 2] JP2002-285140A -   [Patent Document 3] JP2003-3282A -   [Patent Document 4] JP2004-293916A

SUMMARY OF INVENTION Technical Problem

When using an evaporator subjected to hydrophilic treatment as disclosed in the above patent documents, the odor components absorbed on the surface are washed away with the condensed water, and the odor components are less likely to accumulate on the surface of the evaporator. In reality, however, even when an evaporator subjected to such surface treatment is used, people may be able to sense odors at certain timing during the operation of the air conditioner. Thus, the conventional deodorization measures have not necessarily been sufficient.

The present invention has been made in view of such circumstances and an object of the present invention is to provide a heat exchanger capable of deodorization or odor suppression by means of a scheme (mechanism) different from conventional ones.

Solution to Problem

As a result of intensive studies to achieve the above object, the present inventors have newly found that existence of polyamine on the surface of a constitutional material (Al alloy sheet) of a heat exchanger can suppress the odors sensed by people. Developing this achievement, the present inventors have accomplished the present invention as will be described hereinafter.

«Heat Exchanger»

(1) The present invention provides a heat exchanger having a polyamine on at least part of a surface of the heat exchanger.

(2) Existence of polyamine on at least part of the surface of the heat exchanger allows people not to sense odors caused by the heat exchanger in a space in which the air having passed through the heat exchanger can be introduced. The mechanism for obtaining such an effect can be considered as follows at present from the studies on the present invention.

First, people detect even very low-concentration substances (odor components) by smell and sense “odors.” However, the human nose tends to sense odors strongly when the amount (concentration) of odor components or the quality (ratio of each odor component mixed) has changed, rather than sensing the intensity of odors in response to the absolute amount (concentration) of odor components.

Next, in the case of heat exchangers, the release (evaporation) of water plays a large role in the release of odor components. In addition, many of the released odor components are often those absorbed into the water existing on the surface of the heat exchanger from the atmosphere, or the like.

Based on such knowledge and the results of an evaluation test, which will be described later, the polyamine existing on the surface of the heat exchanger temporarily holds the odor components and water to suppress the release thereof and suppresses sudden release of the odor components into an air-conditioned interior room (i.e., releases the odor component slowly). It can thus be considered that, as a result, people in the air-conditioned interior room are less likely to sense the odors caused by the heat exchanger.

«Others»

(1) In the heat exchanger of the present invention, it suffices that the polyamine exists at least on the surface side, and the existence form of the polyamine on the surface of the heat exchanger is not limited. In a general form, the polyamine may often be contained in a polymer film that coats the surface of the heat exchanger. In this case, the polymer film may be composed of a simple substance of polyamine or may also contain a polymer, a resin, a metal, and the like other than the polyamine.

The polyamine as referred to in the present invention may be modified, and part of the terminal groups may be substituted with one or more types of polar functional groups such as a carbonyl group, a carboxyl group, an imide group, a hydroxyl group, a nitrile group, a nitro group, a sulfide group, a sulfoxide group, a sulfone group, a thiol group, and an ester group. The polyamine according to the present invention may be a mixture of two or more types of polymers (high molecules), and one or more types thereof may have a graft polymerization structure.

The polyamine preferably has a chelate structure. Coordination of metal ions can give antiseptic and antibacterial properties and other appropriate properties to the heat exchanger. It is also preferred that the surface of the heat exchanger be given a hydrophilic property. The polyamine itself may exhibit the hydrophilic property, or the polyamine may cooperate with one or more other polymers (high-molecular materials) to give the hydrophilic property to the surface of the heat exchanger.

(2) Unless otherwise stated, a numerical range “x to y” as referred to in the present description includes the lower limit x and the upper limit y. Any numerical value included in various numerical values or numerical ranges described in the present description may be selected or extracted as a new lower or upper limit, and any numerical range such as “a to b” can thereby be newly provided using such a new lower or upper limit.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view illustrating a state in which water molecules are bonded to and incorporated in a molecule of polyethylenimine which is one of polyamines.

FIG. 2A is a set of explanatory views schematically illustrating a mechanism for sensing odors.

FIG. 2B is a set of explanatory views schematically illustrating a mechanism for releasing odor components.

FIG. 3 is a schematic diagram illustrating the overview of an apparatus used in an evaluation test for odors.

FIG. 4 is a graph obtained in the evaluation test according to a first example.

FIG. 5 is a graph obtained in the evaluation test according to a second example.

FIG. 6 is a graph illustrating the thicknesses of hydrated layers on the surfaces of materials under test used in the evaluation test.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

One or more features freely selected from the present description can be added to the above-described features of the present invention. In some cases, methodological features can even be features regarding a product. Which embodiment is the best or not is different depending on the objectives, required performance, and other factors.

«Polyamine» (1) Structure

Polyamine is a polymer having amino groups. Examples of the polyamine include a linear aliphatic hydrocarbon having three or more primary amino groups bonded thereto. A further specific example is polyethylenimine (PEI).

The molecular formula of PEI is (—CH₂—CH₂—NH—)_(n), which has a molecular structure as illustrated in FIG. 1. The main functional group is an amino group (—NH—), which is a polar group. The distance between adjacent amino groups (distance between adjacent N molecules) is about 3.7 Å. The molecular diameter of water that is hydrogen-bonded to the amino group is about 2 Å. From this viewpoint, the distance between adjacent amino groups of the polyamine is preferably 2 to 4 Å and more preferably 2.5 to 3.5 Å in an embodiment.

(2) Water Characteristics

The polyamine exists as if it grows on the base material surface of the heat exchanger, and incorporates one to several molecules of water so as to retain them. The water included in the polyamine is strongly electrically bonded to the polyamine and is not easily separated (evaporated, desorbed, etc.) from the polyamine even when heated to a high temperature, unless heated to a boiling point or higher. On the other hand, on the surface side, condensed water (dew condensation water) or the like that can move freely is easily generated and evaporated in accordance with changes in the environment (temperature and humidity of the atmosphere) to which the surface of the heat exchanger is exposed.

In the present description, as appropriate, water that is incorporated in the polyamine and is not easily released will be referred to as “bound water,” water that is easily generated on the polyamine or easily evaporated from the polyamine will be referred to as “free water,” and water that exists in the transition zone between the bond water and the free water and exhibits intermediate characteristics between the two will be referred to as “intermediate water.” In the case of a heat exchanger (in particular, an evaporator), a typical example of the free water is the “condensed water” (dew condensation water) caused by dew condensation of water vapor in the air, and the intermediate water can be rephrased as “adsorbed water.” In the present description, as appropriate, the term “condensed water” will be used synonymously with the “free water” and the term “adsorbed water” will be used synonymously with the “intermediate water.”

The bound water/intermediate water (also referred to as a hydrated layer) formed on the polyamine has a thickness of preferably 20 to 90 nm and more preferably 30 to 70 nm in an embodiment. An unduly small thickness may deteriorate the slow-release effect, while the bound water/intermediate water having an unduly large thickness may be difficult to form. The thickness of such a hydrated layer bonded on the polyamine can be specified with a scanning probe microscope (SPM).

(3) Odor Characteristics

The odor components can be released, as illustrated in FIG. 2A, on the surface of the base material (e.g., an Al alloy fin) of the heat exchanger. First, when no polyamine exists on the base material surface, as illustrated in FIG. 2A (1), the odor components are in a state of being dissolved, absorbed, and condensed in the free water (e.g., condensed water such as dew condensation water) generated on the base material surface. When the free water evaporates due to a humidity decrease or a temperature increase in the atmosphere to which the base material surface is exposed, the odor components are also released at once into the atmosphere as the free water evaporates. This rapidly increases the concentration of odor components in the atmosphere, so that people present in the atmosphere will strongly sense the odors.

Next, when polyamine exists on the base material surface of the heat exchanger, as illustrated in FIG. 2A (2), the odor components are in a state of being dissolved, absorbed, and incorporated in the free water (e.g., condensed water such as dew condensation water) generated on the base material surface. This is the same as the case in which no polyamine exists.

However, many of the odor components in the state of being absorbed and further condensed are organic substances, and they are often high molecules having polarity in themselves, many of which are in a state of captured by the polar groups of the polyamine due to electrical attraction. As a result, even when the free water existing on the polyamine evaporates, the odor components are not released at once as the free water evaporates. This is one of differences from the case in which no polyamine exists as illustrated in FIG. 2A (1).

Moreover, the intermediate water/bound water remaining in the vicinity of the polyamine after the evaporation of the free water is less likely to evaporate than the free water, and the bound water hardly evaporates. Thus, the odor components, which have moved to the hydrated layer composed of the intermediate water/bound water as the free water evaporates, are also not released into the atmosphere at once. This is another one of differences from the case in which no polyamine exists as illustrated in FIG. 2A (1).

Furthermore, when polyamine exists, water in the hydrated layer evaporates moderately and the odor components continue to be also moderately released as the water evaporates. When polyamine exists, therefore, the odor components are not excessively concentrated in the hydrated layer.

After the free water and the water in the hydrated layer evaporate, when free water is generated again, part of the low-concentration odor components which are temporarily held in the hydrated layer is moved (distributed) to the free water and the odor components come to a further low-concentration state, so the hydrated layer does not continue to accumulate odors.

It appears that such phenomena are repeated on the polyamine existing on the base material surface of the heat exchanger and act synergistically, so that the odor components are not released into the atmosphere at once (i.e., slowly released), and odors that are strongly sensed by people can be suppressed.

(4) Release Behavior of Odor Components on Evaporator

The mechanism in which the existence of polyamine on the base material surface of the heat exchanger allows the odor components to be slowly released (release behavior of the odor components) will be specifically described in detail with reference to FIG. 2B. FIG. 2B schematically illustrates the release behavior of odor components when PEI, which is a typical example of polyamine, exists on an evaporator, which is a typical example of the heat exchanger.

As illustrated in FIG. 2B (1), when the air conditioner is turned on to start the operation of a compressor, the compressed refrigerant expands adiabatically in the evaporator to lower the surface temperature of the evaporator. This cools the air in contact with the surface of the evaporator, and the water vapor contained in the air is condensed into dew on the surface to become the free water (condensed water, dew condensation water). Then, the odor components contained in the air in contact with the evaporator are taken into the free water through dissolution and/or absorption. Part of the odor components taken into the free water also moves to the hydrated layer composed of the intermediate water/bound water just beneath the free water (on the base material surface side). Thus, the concentration of odor components in each type of water comes to an equilibrium state within a range that allows the odor components to be incorporated in the water of each layer.

As illustrated in FIG. 2B (2), when the compressor of the air conditioner stops its operation, the surface temperature of the evaporator starts to rise, and the free water existing on the surface is evaporated (released) accordingly. At this time, the odor components dissolved/absorbed in the free water and odor components in other possible forms are released into the interior room together with the water vapor (water molecules) of the free water. As described above, however, part of the odor components taken into the free water has been transferred (distributed) to the hydrated layer composed of the intermediate water/bound water. As such, highly concentrated odor components are not released into the air-conditioned interior room in conjunction with the evaporation of free water. Furthermore, the hydrated layer composed of the intermediate water/bound water receives the electrical attraction force from the PEI side and is less likely to freely evaporate like the free water. Thus, even when the free water evaporates, the odor components having transferred to the hydrated layer are not released into the interior room at once.

As illustrated in FIG. 2B (3), when the compressor is restarted, free water is generated again on the surface of the evaporator. Odor components contained in the air gradually decrease due to washing or the like of the evaporator surface associated with the outflow of the free water. As a result, when the concentration of odor components taken into the free water also decreases, the odor components which are temporarily held in the hydrated layer move moderately to the free water in an opposite manner, and the concentration of odor components comes to an equilibrium state in whole.

As illustrated in FIG. 2B (4), when the free water evaporates due to stopping the compressor again, the odor components having transferred from the hydrated layer to the free water are also released in conjunction with the evaporation of the free water. As will be understood, the concentration of odor components released at this time is relatively low.

As illustrated in FIG. 2B (5), when the free water evaporates and the amount of the free water decreases, the water in the hydrated layer also starts to gradually evaporate. In conjunction with the evaporation, the odor components contained in the hydrated layer are also released. Also in this case, the concentration of odor components released due to the evaporation is low because the amount of odor components contained in the hydrated layer is not large.

After that, when a hydrated layer is newly generated and odor components are taken in from the air in contact with the evaporator via the free water or the like, part of the odor components is transferred to and held again in the hydrated layer composed of the intermediate water/bound water with a reduced concentration of the odor components. Then, the cycle illustrated in FIG. 2B (1), FIG. 2B (2), etc. described above is repeated again.

In any case, the PEI existing on the base material surface of the evaporator has a polarity capable of temporarily holding the odor components and generates the hydrated layer, and the odor components are thereby prevented from being released into the air-conditioned interior room at once. As a result, the odor components are slowly released into the air-conditioned interior room, the concentration change in the odor components in the air-conditioned interior room becomes moderate, and people in the air-conditioned interior room do not sense strong odors.

(5) Molecular Weight

The reason that the polyamine exhibits the slow-release action for odor components is due to its molecular structure. As the molecular weight changes, the thickness or the like of the hydrated layer changes and the slow-release effect for the odor components can also change. For example, the larger the molecular weight, the larger the thickness of the hydrated layer, and the slow-release effect and therefore the deodorization effect tend to be enhanced. In this context, the molecular weight of the polyamine is preferably 300 to 70,000 and more preferably 400 to 35,000 in an embodiment. Polyamines with an unduly low or high molecular weight are not readily available. From another aspect, an unduly low molecular weight may reduce the slow-release effect while an unduly large molecular weight may increase the viscosity so that the adhesion to the base material surface will be difficult.

The molecular weight as referred to in the present description is a well-known Z-average molecular weight (Mz) and calculated as Mz=ΣMi3Ni/ΣMi2Ni (Mi: each molecular weight, Ni: number of molecules of molecular weight Mi).

(6) Adhesion

The polyamine may exist as a simple substance of polyamine, for example, on the base material surface of the heat exchanger or may also coexist with one or more types of polymers, surfactants, etc., other than the polyamine. Examples of polymers mixed with the polyamine include those having one or more types of polar functional groups such as an amino group, a carbonyl group, a carboxyl group, an imide group, a hydroxyl group, a nitrile group, a nitro group, a sulfide group, a sulfoxide group, a sulfone group, a thiol group, and an ester group.

The adhesion form of the polyamine to the base material surface is not limited. The polyamine may adhere only to the surface layer of a polymer film or adhere to the entire film including the inside of a polymer film or may also be a polymer film composed of a composite component. The region (site) to which the polyamine adheres may be a part or all of the heat exchanger. The heat exchanger is provided with a large number of fine air passages, so a coating method, a dipping method, or the like is appropriately selected as the adhesion (film formation) method for the polyamine in accordance with the shape of the heat exchanger.

«Heat Exchanger»

The heat exchanger includes a flow path through which a heat medium flows and air fins disposed around the flow path. The heat exchanger is typically an evaporator, but may be a condenser, a radiator, or the like as long as deodorization/odor suppression is required, and may not necessarily be used for air conditioning. Furthermore, the heat exchanger and equipment provided with the heat exchanger may be used in any of moving vehicles (such as automobiles, railway vehicles, aircrafts, and ships), homes, business places, and the like.

EXAMPLES

On the assumption that people in an interior room would be less likely to sense odors caused from a car air-conditioner (in particular, from the evaporator), various samples to which odor components were made adhere were prepared and a test was performed to evaluate odors generated from each sample. The present invention will be described in more detail with reference to such specific examples.

First Example «Sample» (1) Base Material

A silicate-based glass plate (simply referred to as a “glass plate”/Sample 11) was prepared as the base material (test piece) to which odor components were to adhere. The size of the base material was 16×76×1 mm.

(2) High-Molecular Film

The surface of the glass plate was coated with a high-molecular film composed of PEI (simply referred to as a “PEI film”). PEI is a typical example of polyamine. The film formation was performed through introducing glycidyltrimethoxysilane into silanol groups on the glass plate surface and making the PEI adhere to the glass plate surface.

(3) Odor Components

Acetic acid, butyric acid, and trimethylamine (TMA) were used as the odor components made to adhere to the base material. These are all typical odor substances composed of organic substances. The base material was immersed in a mixed aqueous solution of these odor components (acetic acid: 1,000 ppm, butyric acid: 100 ppm, TMA: 1,000 ppm) for 3 days. The base material pulled out of the mixed aqueous solution was sufficiently washed with pure water and then naturally dried indoors. The sample thus obtained was subjected to odor evaluation.

«Test»

The release behavior of the odor components according to the sample was checked using a test apparatus as illustrated in FIG. 3. Specifically, first, the sample to which the odor components adhered was put into a glass chamber, and N₂ with conditioned humidity using a mass flow meter and a humidifier was introduced into the chamber. This chamber was alternately immersed in a constant-temperature bath of high-temperature (30° C.) and a constant-temperature bath of low temperature (2° C.) to change the environment in the chamber (temperature and humidity in the vicinity of the surface of the material under test). At that time, the holding time at the high temperature was set to 15 minutes and the holding time at the low temperature was also set to 15 minutes.

For the air having passed through the chamber and led to a discharge port, measurement of humidity change and sensory evaluation (odor intensity evaluation) were performed. Along with the sensory evaluation, the air was collected in a collection tube, and the concentration analysis for each odor component was also performed using a gas chromatography-mass spectrometer (GC/MS). The results thus obtained are illustrated together in FIG. 4.

The upper part of FIG. 4 illustrates the humidity of the air introduced into the chamber (WET/DRY), the holding temperature of the chamber, and the humidity of the air led out from the discharge port (sensory evaluation port). The middle and lower parts of FIG. 4 illustrate the sensory evaluation results and the GC/MS measurement results obtained, respectively, for Sample 11 (with a PEI film) and Sample C0 (an aluminum alloy sheet with no PEI film/details will be described later).

«Evaluation»

As apparent from FIG. 4, it has been revealed that the release behavior of odor components differs depending on the presence or absence of the PEI film. Specifically, Sample 11 with the PEI film showed a moderate change in both the odor component concentration in the GC/MS and the sensory evaluation as compared with Sample C0 with no PEI film. That is, it has been revealed that the odor components are slowly released by virtue of the PEI film and the odors are thereby less likely to be sensed.

Second Example «Samples»

An aluminum alloy sheet (simply referred to as an “Al alloy sheet”/Sample C0) was prepared as the base material to which odor components were to adhere. This Al alloy sheet may be used for a heat exchanger (evaporator) and is obtained by surface-treating an aluminum alloy (A1050) with a hydrophilic resin. The size of the base material was 16×76×0.2 mm.

In addition to the Al alloy sheet (Sample C0), Sample 21 and Sample 22 were also prepared by coating the surfaces of respective Al alloy sheets with high-molecular films (PEI films) having different molecular weights (PEI molecular weight for Sample 21: 600, PEI molecular weight for Sample 22: 10,000).

The odor components were made to adhere to the sample in the same manner as in First Example. The sample thus obtained was subjected to odor evaluation.

«Test»

(1) The same sensory evaluation (odor intensity evaluation) as in the case of First Example was performed for each material under test. The obtained results are illustrated together in FIG. 5. The upper part of FIG. 5 illustrates the temperature of the chamber and the humidity of the discharge port (sensory evaluation port). The lower part of FIG. 5 illustrates the sensory evaluation result according to each sample.

(2) The thickness of a hydrated layer existing on the surface of the material under test of each sample (before the sensory evaluation test) was measured using an atomic force microscope (AFM: SPM-8000FM available from Shimadzu Corporation), which is a kind of scanning probe microscope (SPM). The results thus obtained are illustrated in FIG. 6.

«Evaluation»

(1) As apparent from FIG. 5, Sample C0 with no PEI film showed a sharply peaked odor intensity. On the other hand, in Samples 21 and Sample 22 with the PEI films, the odor intensity was significantly reduced and the change in the odor intensity was moderate. This tendency was more prominent in the sample with a larger amount of amino groups introduced.

(2) From FIG. 6, it has been found that the thicknesses of hydrated layers generated on the surfaces of the materials under test were 9 nm in Sample C0, 30 nm in Sample 21, and 50 nm in Sample 22. It has thus been revealed that as the molecular weight of PEI increases, the thickness of the hydrated layer formed on the surface of the material under test also increases, so that the odor intensity is reduced and the change in the odor intensity is suppressed.

(3) Furthermore, from FIG. 5, it has also been revealed that the timing at which the odor intensity reaches the maximum (peak) is different in each sample. Specifically, in Sample C0 with no PEI film, the odor intensity was maximized in the vicinity of a time point at which the humidity of the discharge port was maximized. On the other hand, in Samples 21 and 22 with the PEI films, the time when the odor intensity was maximized was delayed from the time when the humidity of the discharge port was maximized. As previously described, the maximum values of Samples 21 and 22 were significantly reduced as compared with Sample C0.

(4) The reason that such a tendency was obtained is considered as follows. In Sample C0 with no PEI film, it appears that the release of odor components is in conjunction with the evaporation of water from the surface of the material under test. On the other hand, in Samples 21 and 22 with the PEI films, it appears that the release of odor components is not necessarily in conjunction with the evaporation of water and the odor components continue to be moderately released (i.e., slowly released) by virtue of the PEI films.

Moreover, as the sample is formed with PEI having a higher molecular weight, the maximum value of the odor intensity is reduced and the timing at which the odor intensity is maximized is delayed. One reason for this appears to be because the higher the molecular weight of PEI, the thicker the hydrated layer can be formed on the base material surface, and a larger amount of odor components can be temporarily held.

In any case, it has been revealed that the existence of the polyamine on the base material surface of the heat exchanger allows the odor components to be moderately released (slowly released), and even when the ambient environment (such as humidity and temperature) changes, the odor components are not rapidly released, so that the odors which are strongly sensed by people can be suppressed. 

1. A heat exchanger having a polyamine on at least part of a surface of the heat exchanger.
 2. The heat exchanger as recited in claim 1, wherein the polyamine has a molecular weight of 300 to 70,000.
 3. The heat exchanger as recited in claim 1, wherein the polyamine has a distance of 2 to 4 Å between adjacent amino groups.
 4. The heat exchanger as recited in claim 1, wherein the polyamine includes a hydrated layer having a thickness of 20 to 90 nm.
 5. The heat exchanger as recited in claim 1, wherein the polyamine is a polymer having one or more types of functional groups selected from a carbonyl group, a carboxyl group, an imide group, a hydroxyl group, a nitrile group, a nitro group, a sulfide group, a sulfoxide group, a sulfone group, a thiol group, or an ester group.
 6. The heat exchanger as recited in claim 1, wherein the polyamine comprises at least polyethylenimine (PEI).
 7. The heat exchanger as recited in claim 1, wherein the heat exchanger is an evaporator. 